Impairment discovery is increasingly problematic as cable infrastructure becomes more ubiquitous. Network impairments can cause noisy or blocky TV pictures, unintelligible telephone conversations, slow web page downloads, or impaired 2-way communications. Outages are one of several types of impairments. Other types of impairments are high transmit level, low receive level, low modulation error rate (MER), continuous wave interference, and non-linear and linear distortions.
Currently, the most popular cable architecture is a hybrid fiber coax (HFC) architecture. An HFC architecture can employ fiber optic cable for the long distance from a hub (or headend) site to a node. A hub site is a source point for downstream signals and a destination point for upstream signals. A node is a grouping of approximately 500 homes. Inside a node the signals are distributed via coaxial cable to a terminal device, which is typically located inside a home, apartment, or office. A terminal device can be a cable modem (CM), multimedia terminal adapter (MTA), set-top box (STB), or gateway device. A coaxial portion of the cable plant is built with a tree-and-branch architecture, so an impairment on a branch can potentially affect multiple subscribers.
Impairments can be discovered using a network monitoring software, which communicate with the subscriber's equipment. One current method to find impairments is to provide a connectivity database where a list of terminal devices attached to each branch is supplied. When an impairment occurs, a defective branch can be located using a list of affected customers. However, connectivity databases can be costly to maintain and are frequently out-of-date.
Another method to find impairments uses colored pins on a map to identify subscribers without service. Cable operator databases show addresses for subscribers and can also show latitude and longitude coordinates. If a number of colored pins are noticed to form a cluster, an impairment can be declared. However, this method requires operators to stick the pins into a map and visually identify an impairment. Random isolated outages are generally ignored because they can be caused by a subscriber unplugging the terminal equipment to save electricity.
Like reference numbers and designations in the various drawings indicate like elements.